Magnetic recording systems

Abstract

A digital magnetic recording system in which information is recorded as transitions between regions magnetized in opposite senses. In the read channel the output of the read head is applied to modulate a carrier, passed through a surface acoustic wave transversal filter and then demodulated, and the resulting transformed waveform is sampled. The surface acoustic wave transversal filter is designed to control the manner in which the transformed versions of elementary read pulses interfere at the sampling instants in such a way as to facilitate recovery of the recorded bits.

I claim: 
     
       1. Apparatus for reproducing digital information recorded on a magnetic medium as transitions between regions of the medium magnetised in opposite senses, the apparatus comprising: a read head for outputting a read waveform on relative movement between the magnetic medium and the read head, the read waveform being composed of read pulses each resulting from the relative movement of a single one of the said transitions past the read head, and read pulses being subject to interference with one another;   means for transforming the read waveform into a transformed waveform, which means comprise in sequence a modulator arranged to modulate a carrier wave in accordance with an input derived from the output of the read head, surface acoustic wave transversal filter means and a demodulator arranged to remove the said carrier wave; and   means for extracting from the transformed waveform a digital signal dependent on the recorded information;   the response of the surface acoustic wave transversal filter means being such as to facilitate the extraction of the said digital signal by controlling the manner in which, or at least reducing the extent to which, the transformed versions of the read pulses interfere with one another.   
     
     
       2. Apparatus as claimed in claim 1, in which the transistions on the recorded medium are arranged in operation to occur at selected ones of a plurality of evenly spaced positions on the medium and the extracting means includes sampling means for sampling the amplitude of the transformed waveform at a plurality of sampling times, the characteristics of the transformation of the read waveform into the transformed waveform being such that an isolated read pulse is transformed into a pulse the amplitude of which, as sampled at each sampling time, is substantially zero or bears a substantially predetermined relation to a reference value. 
     
     
       3. Apparatus as claimed in claim 2, in which the sampling means is arranged to carry out the sampling at the same rate that the positions on the medium at which transitions can occur in operation pass relative to the read head. 
     
     
       4. Apparatus as claimed in claim 1, in which the transforming means output a rectified waveform. 
     
     
       5. A method of reading digital information recorded on a magnetic medium as transitions between regions of the medium magnetised in opposite senses, the method comprising: causing relative movement between the magnetic medium and a read head, the read head being thereby caused to output a read waveform composed of read pulses each resulting from the relative movement of a single one of the said transitions past the read head, read pulses being subject to interference with one another;   transforming the read waveform into a transformed waveform by means which comprise in sequence a modulator in which a carrier wave is modulated in accordance with an input derived from the output of the read head, surface acoustic wave transversal filter means and a demodulator in which the said carrier wave is removed;   and extracting from the transformed waveform a digital signal dependent on the recorded information;   the response of the surface acoustic wave transversal filter being such as to facilitate the extraction of the said digital signal by controlling the manner in which or at least reducing the extent to which, the transformed versions of the read pulses interfere with one another.   
     
     
       6. A method as claimed in claim 5, in which the said transitions on the magnetic medium occur at selected ones of a plurality of evenly spaced positions on the medium and the extraction step includes sampling the amplitude of the transformed waveform at a plurality of sampling times, the characteristics of the transformation of the read waveform into the transformed waveform being such that an isolated read pulse is transformed into a pulse the amplitude of which, as sampled at each sampling time, is substantially zero or bears a substantially predetermined relation to a reference value. 
     
     
       7. A method as claimed in claim 6, in which the sampling is carried out at the same rate as the positions on the magnetic medium at which transitions can occur pass relative to the head. 
     
     
       8. A method as claimed in claim 5, in which the transforming step produces a rectified waveform.